The present invention relates to method for recording, reproducing and erasing information by irradiating an energy beam such as a light or electron beam onto an information recording medium, and more particularly to method for recording, reproducing and erasing information by a single beam spot by using a phase change and an information recording medium which is effective for use in the above method.
A prior art method for recording, reproducing and erasing information in a phase change type optical disk is shown in JP-A-59-71140 in which recording is done by irradiating a small circular light spot formed by fully focusing a light beam spot for a short time period to render a recording film to a complete amorphous state by quick heating and cooling, and erasing is done by irradiating an elliptical light spot extending along a track to keep the recording material at a crystallization temperature for a relatively long time so that the amorphous state recorded area is returned to a complete crystalline state. Thus, two different beam spots are used for recording and reproducing.
A second prior art method is disclosed in JP-A-56-148740 in which a single light beam spot is used to erase recorded information in one or a plurality of revolutions of a disk medium and record information in the next revolution.
A third prior art method is disclosed in JP-A-56-145530 in which a light which is intensity modulated between at least two power levels is irradiated to simultaneously record and erase information.
In the first method, since two beam spots are used, two light sources are necessary and an optical system is complex.
In the second method, it is necessary to rotate the disk medium a number of revolutions to update the information, and hence it takes a long time.
In the third method, the above problems are resolved but it is necessary to completely crystallize the recording film prior to recording, and tracking at a reproduction power level, automatic focusing and track or sector address confirmation prior to recording are not effected. Further, since an initial power level is not always an erase power level, a leading portion of the previously written information will not be updated if a start position of updating is deviated.
On the other hand, a recording thin film for the phase change type optical disk is disclosed in JP-B-47-26897 which also describes various thin films such as Te-Ge, As-Te-Ge and Te-O. JP-B-54-41902 discloses various compositions such as Ge.sub.10 Tl.sub.4 Sb.sub.5 Se.sub.70 and Ge.sub.20 Bi.sub.10 Se.sub.70. JP-A-57-24039 discloses thin films of Sb.sub.25 Te.sub.12.5 Se.sub.62.5, Cd.sub.14 Te.sub.14 Se.sub.72, Bi.sub.2 Se.sub.3, Sb.sub.2 Se.sub.3, In.sub.20 Te.sub.20 Se.sub.60, Bi.sub.25 Te.sub.12.5 Se.sub.62.5, CuSe and Te.sub.33 Se.sub.67.
However, in the prior art, when the rewritable phase change type recording thin film is used, a crystallization rate is low, a semiconductor laser beam is not well absorbed and a sensitivity is low, a reproduced signal intensity is not sufficient, a stability of the amorphous state is low or resistance to oxidation is insufficient.